Dude you write at length about all the reasons to not use Holliday before September. But you skip right over the most obvious reason to put him on the roster prior to September.
Win freaking baseball games.
Dude doesn't think he will be appreciably better than the alternatives this year because of youth and inexperience. If he's barely better than guys like Ortiz and Westburg in 2024, might as well get an extra year on the back end when he's in his prime.
He'll be approximately 20 and 4 months on OD. Gunnar was ~21 and 2 months when he debuted. Carroll was 22 when he debuted. They were HS draftees and #1/#2 prospects.
I don't have a problem with that argument. I don't agree that it's "entirely unlikely that he can produce" what Frazier and Mateo did, I.e. can't manage a 700 OPS, but I want to wait and see how spring goes. If you think he has a chance at a breakout 5 WAR year you obviously want him on the team.